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NDVI June, 2009
Mid-latitude Afforestation: Consequences for General Circulation and Tropical Precipitation
1Harvard University, Organismic and Evolutionary Biology Dept. & Sustainability Science Prgm., Harvard Kennedy School2 University of California Berkeley, Dept. Earth & Planetary Science3 University of California Berkeley, Dept. of Geography
Abigail Swann1, Inez Fung2, John Chiang3
Land Model Working Group Meeting, March15th, 2011
Mid Latitude Ecosystems
NDVI June, 2009
model: National Center for Atmospheric Research Community Climate ModelAtmosphere: CAM 3.0, Land:CLM 3.5, run w/ CASA’ (biogeochemistry)Resolution: T42 L26Ocean: Slab Ocean Model
model spin-up: Land and carbon pools are set to equilibrium values from a long control run with fixed observed SST.
CO2 held fixed at 355ppm for all present day runs
equilibrium experiments: runs are 120 years, results averaged over 100 years.
Global Climate Model Details
Percent of gridcell afforested
0 12.5 25 37.5 50 62.5 75 87.5 100% of gridcellTotal area converted = 2.1 x 107 km2
Crops and C3 grass ⇒ Broadleaf Decid. Trees
Swann et al., in review
Mid Latitude Afforestation
NDVI June, 2009
Consequences of expanding deciduous tree cover in mid latitudes?
a. Climate response to afforestationb. Tropical circulation responsec. Implications for climate management
Surface Temp. Increases with Mid Latitude Trees
Kelvin
annual mean
K
Swann et al., in review
Trees
Trees Lower Albedo ⇒ More Absorbed Solar S
W N
et F
lux (
Wm
)
Latitude (deg)
Clear Sky Net Short Wave Flux at the Surface
DJF
MAM
JJA
SON
Swann et al., in review
Trees
Trees Lower Albedo ⇒ More Absorbed Solar
Sea Ice Loss
SW
Net F
lux (
Wm
)
Latitude (deg)
Clear Sky Net Short Wave Flux at the Surface
DJF
MAM
JJA
SON
Swann et al., in review
Sensible Heat
Short Wave
Latent Heat
Long Wave
Terrestrial Surface Energy Budget
Atmospheric Water Supply Gap
1− ET
PET
Measures the inability of the surface to meet the water demands of the atmosphere.
Widening Gap
Narrowing Gap∆(1− ET
PET) < 0
∆(1− ET
PET) > 0
Water Supply Gap
WET DRY
JJA
Swann et al., in review
Sensible Heat
Short Wave
Latent Heat
Long Wave
Terrestrial Surface Energy Budget
Sensible Heat removes absorbed Short Wave
5−12−20101 2 3 4 5 6 7 8 9 10 11 12
−0.02
0
0.02
0.04
0.06
0.08
Month
Δ T
herm
al R
atio
Climatology of ΔThermal Ratio
ΔV−IO+/− 1 σ
Short Wave
Sens
ible
Hea
tMid Latitiude Afforested points, JJA
Solar Absorbed at the Surface (Wm )
Sensib
le H
eat F
lux (
Wm
)
Swann et al., in review
Sensible Heat removes absorbed Short Wave
5−12−20101 2 3 4 5 6 7 8 9 10 11 12
−0.02
0
0.02
0.04
0.06
0.08
Month
Δ T
herm
al R
atio
Climatology of ΔThermal Ratio
ΔV−IO+/− 1 σ
Short Wave
Sens
ible
Hea
tMid Latitiude Afforested points, JJA
Solar Absorbed at the Surface (Wm )
Sensib
le H
eat F
lux (
Wm
)1:1 line
Swann et al., in review
Latent heat is curtailed by water limitation
Sensible heat removes most of the extra energy
Temperature increases most where water is limited
Mid Latitude Afforestation
dry ⇒ hot
Latent heat is curtailed by water limitation
Sensible heat removes most of the extra energy
Temperature increases most where water is limited
Mid Latitude Afforestation
dry ⇒ hot
⇒ soil moisture controls
the surface temperature response
NDVI June, 2009
1. Climate response to Forests2. Tropical Circulation and Precipitation3. Implications for climate management
Mid Latitude Afforestation
mm/day
Mid Latitude Trees modify Tropical Precipitation
mm/day
annual mean
WETDRYSwann et al., in review
mm/day
mm/dayWETDRY
mm/day
annual mean
Mid Latitude Trees modify Tropical Precipitation
Swann et al., in review
Hadley Circulation Streamfunction
ERA-40 Atlas0
0
0
0
0
00
0
0
0
0
0
0
00
00
0
-50
-50
-50
-50
-10
-10
-10
-10
-10
-10
-10
-10
-10
-10
-10
55
5
5
5
5
5
5
5
5
5
30
30
3030
3030
1000
900
800
700
600
500
400
300
200
100
80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS
Annual mean
-300-250-200-150-100-75-50-30-20-10-5
Pre
ssur
e (h
Pa)
Mean meridional streamfunction109 kg/sec
51020305075100150200250300
NORTH SOUTH
Winter Cell Does the Transport0
0
00
0
0
0
0
0
0
0
0
00
0
0
00
-10
-10
-10
-10
-10
-10
-10
-10
-10
5
5
5
5
5
5
5
5
5
5
5
30
30
30
30
30
30
30
100
100
100
100
1000
900
800
700
600
500
400
300
200
100
80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS
December-February
-300-250-200-150-100-75-50-30-20-10-5
Pre
ssur
e (h
Pa)
Mean meridional streamfunction
109 kg/sec
51020305075100150200250300
0
00
0
0
0
0
0
0
0
0
0
0
00
-150
-150
-50
-50
-50
-50
-10
-10
-10
-10
-10
-10
-10
-10
-10
-10
-10
5
5
5
5
5
5
5
5 30
30
1000
900
800
700
600
500
400
300
200
100
80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS
June-August
-300-250-200-150-100-75-50-30-20-10-5
Pre
ssur
e (h
Pa)
Mean meridional streamfunction
109 kg/sec
51020305075100150200250300
NH Summer
NH Winter
ERA-40 Atlas
NORTH SOUTH
Winter
WinterSummer
Summer
0
0
0
0
0
00
0
0
0
0
0
0
00
00
0
-50
-50
-50
-50
-10
-10
-10
-10
-10
-10
-10
-10
-10
-10
-10
55
5
5
5
5
5
5
5
5
5
30
30
3030
3030
1000
900
800
700
600
500
400
300
200
100
80ON 60ON 40ON 20ON 0O 20OS 40OS 60OS 80OS
Annual mean
-300-250-200-150-100-75-50-30-20-10-5
Pre
ssur
e (h
Pa)
Mean meridional streamfunction109 kg/sec
51020305075100150200250300
NORTH SOUTH
NORTH SOUTH
1. dark trees = NH warm*because the surface is water limited*
Hypothesized Mechanism
20eq 6040
20eq 6040
grass
treesHOT
Hypothesized Mechanism
20eq 6040
20eq 6040
grass
treesHOT
1. dark trees = NH warm
2. Energy gradient (N-S) between the Hemispheres increases
1. dark trees = NH warm
2. Energy gradient (N-S) between the Hemispheres increases
3. Hadley Cell moves north to increase southward heat transport
Hypothesized Mechanism
20eq 6040
20eq 6040
grass
trees
Nor
thw
ard
ATM
Tra
nspo
rt (P
W)
Latitude (deg)
Total Northward Atmospheric Energy Transport
Circulation shift moves energy Southward
Southward Energy flux0.17 PW Anomaly
13% change at the Equator
Swann et al., in review
1. dark trees = NH warm
2. Energy gradient (N-S) between the Hemispheres increases
3. Hadley Cell moves north to increase southward heat transport
4. ITCZ shifts North
Hypothesized Mechanism
20eq 6040
20eq 6040
grass
trees
1. dark trees = NH warm
2. Energy gradient (N-S) between the Hemispheres increases
3. Hadley Cell moves north to increase southward heat transport
4. ITCZ shifts North
Hypothesized Mechanism
20eq 6040
20eq 6040
grass
treesTropical productivity follows changes in precipitation
⇒
g/C/m
annual mean
gC/m2/yr
NPP
Mid Lat. Afforestation modifies Tropical Productivity
Swann et al., in review
1. dark trees = NH warm
2. Energy gradient (N-S) between the Hemispheres increases
3. Hadley Cell moves north to increase southward heat transport
4. ITCZ shifts North
Hypothesized Mechanism
20eq 6040
20eq 6040
grass
treesTropical productivity follows changes in precipitation
⇒
NDVI June, 2009
1. Climate response to Forests2. Tropical Circulation and Precipitation3. Implications for climate management
Mid Latitude Afforestation
Afforestation Carbon Budget
Change in Carbon Pools:
∆M Afforested: 270 PgC
∆M Mid-lat: -3 PgC
∆M High-lat: -28 PgC
∆M Tropics: -9 PgC
Total ∆M: 228 PgC
Carbon is taken up by switching from grass to trees, 1/2 above ground
1/2 below ground
2 PgC => 1ppm
ΔCarbon ~ 228 PgC
2 PgC => 1ppm
-114 ppm -2.23-2.1 Wm-2ΔCO2: Δclimate forcing:
Climate Response to ΔCarbon
ΔCarbon ~ 228 PgC
2 PgC => 1ppm
-114 ppm -2.2 Wm-2ΔCO2: Δclimate forcing:
Climate Response to ΔCarbon
-1.10 ˚C ΔT:assume climate feedback: 0.5 degrees/Wm-2 (2 ˚C for 2xCO2)
0.75 degrees/Wm-2 (3 ˚C for 2xCO2)
1 degrees/Wm-2 (4 ˚C for 2xCO2)
-1.65 ˚C
-2.20 ˚C
ΔCarbon ~ 228 PgC
2 PgC => 1ppm
-114 ppm -2.2 Wm-2ΔCO2: Δclimate forcing:
Climate Response to ΔCarbon
-1.10 ˚C ΔT:assume climate feedback: 0.5 degrees/Wm-2 (2 ˚C for 2xCO2)
0.75 degrees/Wm-2 (3 ˚C for 2xCO2)
1 degrees/Wm-2 (4 ˚C for 2xCO2)
-1.65 ˚C
-2.20 ˚C
Equilibrium Experiment:
if we account for ocean response, the net drawdown of atmospheric CO2 is only 14%-40% =>~16-46ppm.
ΔCarbon ~ 228 PgC
2 PgC => 1ppm
-114 ppm -2.2 Wm-2ΔCO2: Δclimate forcing:
Climate Response to ΔCarbon
-1.10 ˚C ΔT:assume climate feedback: 0.5 degrees/Wm-2 (2 ˚C for 2xCO2)
0.75 degrees/Wm-2 (3 ˚C for 2xCO2)
1 degrees/Wm-2 (4 ˚C for 2xCO2)
-1.65 ˚C
-2.20 ˚C
Equilibrium Experiment:
if we account for ocean response, the drawdown of atmospheric CO2 is only 30Pg/15ppm.
Climate Response from ΔCO2 ~ -0.2 to -0.7 ˚C
Climate Response from albedo and transpiration = + 0.3 ˚C
Afforestation leads to little temperature change, but gradients in temperature can still drive
changes in circulation and precipitation
NDVI June, 2009
1. Climate response to mid latitude Afforestation• Soil moisture status controls climate response (dry = hot)
2. Tropical Circulation and Precipitation• Circulation shifts northward to transport more energy to the south
3. Implications for Future Climate• Circulation could still change despite global ∆T
Mid Latitude Afforestation
Latent Heat fluxes occur where water is not limited
5−12−20101 2 3 4 5 6 7 8 9 10 11 12
−0.02
0
0.02
0.04
0.06
0.08
Month
Δ T
herm
al R
atio
Climatology of ΔThermal Ratio
ΔV−IO+/− 1 σ
Long Wave
Late
nt H
eat
Mid Latitiude Afforested points, JJA
Net Longwave at the Surface (Wm )
Late
nt H
eat F
lux (
Wm
)
Latent Heat fluxes occur where water is not limited
5−12−20101 2 3 4 5 6 7 8 9 10 11 12
−0.02
0
0.02
0.04
0.06
0.08
Month
Δ T
herm
al R
atio
Climatology of ΔThermal Ratio
ΔV−IO+/− 1 σ
Long Wave
Late
nt H
eat
Mid Latitiude Afforested points, JJA
Net Longwave at the Surface (Wm )
Late
nt H
eat F
lux (
Wm
)
1:1 line
2−15−2011
PRECIP somcontrol annual mean
0 1 2 3 4 5 6 7 8 9 10
2 4 6−90−75−60−45−30−15
0153045607590
mm/day
Annual Mean Precipitation
mm/day